Kevin is right - West Stand lower tier but i think it is M5 or M6. I suggest you google Twickenham Seating plan. Tickets will be hard to come by at any prt of the ground for an England game.

Yes, I've only ever been for rugby but you can leave early

Exiting the stadium takes no time at all. 10-15 minutes at the most. All stadium have to be in a position to be cleared quickly after events such as Hillsborough and Twickenham is no exception. The delays come at either the train station, the bus stop or car park. Additional trains are rarely added for these events and you may run into night time schedules. Twickenham station is still being developed and buses will be stuck in the additional event day traffic. You could consider walking to another local station (the one before Twickenham) to try and beat the crowds.

We walked up but there are lifts but obviously use these if necessary. It is a bit "up in the Gods" but there is an excellent view. Always ask on arrival about anything that you need to know. Website too is excellent.

sorry i don't know...

I’ve taken a small umbrella in ok.

I thought it was card only. But can’t be 100% sure.

I personally would get the tube to Waterloo then the Overground from there. The advantage of this route is that it’s the start of the line and so more or less guaranteed a seat whereas if you join the train later down its journey that’s not always the case

Yes - lots of fans come in their clubs jersey